Cannot add domain: '"subdomain.domain.tld" is already a dynamic DNS domain.

Symptoms

When attempting to add an addon domain in a cPanel account, you receive an error similar to the following.

"subdomain.domain.tld" is already a dynamic DNS domain. Because this domain is a subdomain of “domain.tld”, you cannot create a DNS zone with that name.

Description

When an addon domain is created, a subdomain of the account's primary domain is created that the addon domain is parked on. The error occurs if the new subdomain has already been added as a Dynamic DNS domain. To add the domain, the Dynamic DNS domain must be removed first.

Workaround

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Locate the Dynamic DNS ID.

   [root@server ~]cPs# ls /var/cpanel/webcalls/user/$pausername/
   syoucgwrdowfwnsuvwmsnubdxavjpgko

   Please note that "$cpusername" must be replaced with the cPanel user's username.
3. Use the UAPI to delete the Dynamic DNS domain.

   [root@server ~]cPs# uapi --user=$cpusername DynamicDNS delete id='$ddnsid'
   --- 
   apiversion: 3
   func: delete
   module: DynamicDNS
   result: 
     data: 
       deleted: 1
     errors: ~
     messages: ~
     metadata: {}
   
     status: 1
     warnings: ~

   Please note that "$cpusername"  and "$ddnsid" must be replaced with the cPanel user's username and the Dynamic DNS ID.

Additional resources

Delete Dynamic DNS domain